The long-term objectives of this project are to study the intraoral demineralization and remineralization of tooth enamel, and to determine the effects that foods and therapeutic agents can have on these processes. The delta Ip system presents a model that is highly useful for studies of this nature. Thus, the relatively rapid response of the system, the sensitivity to single acidogenic challenges, and the possibility to correlate changes in the mineral with changes in plaque, will provide new information that cannot be obtained with other systems. The delta Ip system involves measurements of changes in iodide ion penetrability of enamel following de- or remineralization. For intraoral use, blocks of bovine enamel will be coated with Streptococcus mutans IB1600 and mounted in palatal appliances that will be worn by human volunteers for defined times. Changes in Ip, plaque pH, and calcium and phosphate concentrations in plaque will be followed. Studies are proposed to determine whether soluble calcium or phosphate salts, when incorporated into solid foods, reduce enamel demineralization otherwise induced by the foods. Retained food particles containing such salts should elevate mineral ion concentration in the plaque. Since earlier experiments showed that calcium diffused rapidly from plaque, it is proposed that to be maximally effective, levels of plaque ions must be sustained at least during periods of maximum acidogenicity. The proposed studies will test this hypothesis. Separate experiments will examine the role that plaque fluoride plays in reducing demineralization. We will administer fluoride to subjects, then systematically replace fluoride-exposed plaque or enamel with fluoride-free preparations and determine the effects of each in the delta Ip system. We will also determine the conditions under which fluoride is translocated between plaque and enamel. Finally, experiments will be carried out to determine optimal concentration of calcium, phosphate and fluoride ions for the intraoral remineralization of in vitro demineralized enamel. Since the delta Ip system can detect minimal degrees of surface change (equivalent to the very early stages in caries formation), comparisons will be made between rates of remineralization of surface-and subsurface-demineralized enamel. A finding of such differences could alter the way we approach future studies in cariology.